Polycyclic Aromatic Hydrocarbons (PAHs) are a group of compounds that pose many health threats to human and animal life. They occur in nature as a result of incomplete combustion of organic matter, as well as from many anthropogenic sources including cigarette smoke and automobile exhaust. PAHs have been reported to cause liver damage, red blood cell damage and a variety of cancers. Because of this, methods to reduce the amount of PAHs in the environment are continuously being sought. The purpose of this study was to find soil bacteria capable of degrading high molecular weight PAHs, such as pyrene (Pyr) and benzo[a]pyrene (BaP), which contain more than three benzene rings and so persist in the environment. Bacillus subtilis, identified by fatty acid methyl ester (FAME) analysis, was isolated from PAH contaminated soil. Because it grew in the presence of 33μg/ml each of pyrene, 1-AP and 1-HP, its biodegradation capabilities were assessed. It was found that after a four-day incubation period at 30oC in 20μg/ml pyrene or benzo[a]pyrene, B. subtilis was able to transform approximately 40% and 50% pyrene and benzo[a]pyrene, respectively. This is the first report implicating B. subtilis in PAH degradation. Whether or not the intermediates resulting from the transformation are more toxic than their parent compounds, and whether B. subtilis is capable of mineralizing pyrene or benzo[a]pyrene to carbon dioxide and water, remains to be evaluated.

Application of biochar has been suggested as a carbon (C) management strategy to sequester C and enhance soil quality. An incubation study was carried out to investigate the interactive effect of biochar and cattle manure application on mineralization of carbon (C) in a tropical coastal savanna sandy soil. The soils were amended with three sole levels of cattle manure (0, 13 and 26 tons ha⁻¹) or biochar (0, 20 and 40 tons ha⁻¹) and four combined manure–biochar levels (20 or 40 tons ha⁻¹ biochar plus 13 or 26 tons ha⁻¹ manure) and CO₂ evolution was measured over 56 days incubation period. The soils were analyzed for mineral N (NH₄⁺-N and NO₃⁻-N) and water extractable organic C, and net N mineralization, and priming effect (PE) values calculated. The cumulative C mineralized increased in the sole manure and biochar amended soils, resulting in 45–125% positive PE. However, co-application of biochar and manure decelerated decomposition of C, probably through adsorption of labile C and net N immobilization, subsequently leading up to negative 35% PE. The results suggest that co-application of biochar and cattle manure can potentially stabilize C in manure amended sandy soils, albeit with a temporary mineral N limitation to plants.